CNC machining is one of the core processes of modern manufacturing, covering a variety of cutting methods from turning, milling, drilling to boring. In actual production, it is impossible for us to complete all dimensional requirements in one processing, so it is usually divided into two stages: roughing and finishing . Roughing is mainly used to quickly remove materials and improve production efficiency, while finishing is used to improve the dimensional accuracy and surface quality of parts. I will explore the core differences between roughing and finishing , and combine it with actual application scenarios to help you better understand the role and optimization strategies of these two processing methods.

What Is CNC Rough Machining

Rough machining is the first step in CNC machining. Its main purpose is to remove excess material from the workpiece surface to make its shape close to the final design requirements, while reducing the workload of subsequent finishing. During rough machining, we usually use a larger cutting depth, high feed rate and faster spindle speed to increase the material removal rate. However, due to the large machining parameters, the surface of the rough-machined parts is relatively rough and the dimensional accuracy is also low, so subsequent finishing is required to further improve the quality.

In practical applications, rough machining is widely used in mold manufacturing, aerospace parts processing, automotive parts manufacturing and other industries. For example, in mold manufacturing, we usually need to rough-machine the metal block first, remove the material to a near-final shape, and then perform fine machining to ensure the fit accuracy and surface quality of the mold.

Characteristics Of CNC Rough Machining

The main characteristics of roughing are efficient material removal, but the surface quality is poor and usually cannot meet the requirements of final use. The following are some key characteristics of roughing:

• High material removal rate: Roughing uses a large cutting depth (usually 5-15mm) and a high feed rate (1000-3000mm/min) to remove a large amount of material in a short time.
• Low surface finish: Due to the large feed rate and obvious cutting texture, the surface roughness after rough machining is generally Ra 3.2μm – 12.5μm, which is far from meeting the requirements of precision machining.
• Low dimensional accuracy: Due to the large cutting force, the workpiece may be deformed, resulting in a large dimensional tolerance, usually within the range of ±0.1mm – ±0.5mm.
• The tool load is large: Due to the large amount of cutting, the tool wears faster, so it is necessary to reasonably select the tool material, such as carbide tools or ceramic tools, to extend the tool life.

Typical Parameters For CNC Rough Machining

In actual production, rough machining of different materials requires different cutting parameters to ensure machining efficiency and tool life. For example:

Tool Selection For Roughing

Roughing often uses larger diameter tools to increase cutting efficiency and reduce machining time. Common tool types include:

• Rough milling cutter: suitable for large-area cutting, such as machining of machine tool bases or mold blanks.
• Ball end milling cutter: suitable for rough machining of free-form surfaces, such as contour machining of aerospace parts.
• Carbide end mills: suitable for high-speed machining, especially for materials with high requirements for wear resistance.
• Wave edge milling cutter: suitable for rough machining of hard materials, can reduce cutting vibration and improve machining stability.

In an aviation parts processing project I participated in, we needed to process a 7075 aluminum alloy wing bracket. Due to the hard material and large part size (300mm x 200mm x 50mm), we chose a 20mm diameter carbide end mill, with a 7mm cutting depth and a feed rate of 1800mm/min for rough machining. In just 15 minutes, 90% of the excess material was removed, and the initial contour of the part was formed, which greatly improved production efficiency.

In general, rough machining is a crucial step in CNC machining, which lays the foundation for subsequent finishing. If the rough machining strategy is unreasonable, it may lead to increased tool wear, workpiece deformation and even machine damage. Therefore, during the rough machining process, we must fully consider factors such as cutting parameters, tool selection, machine tool rigidity, cooling system, etc. to ensure the best machining effect.

What Is CNC Finishing

Finishing is the last step of CNC machining, and its main purpose is to improve the dimensional accuracy, surface finish and mechanical properties of parts to ensure that the final product meets the design requirements. Finishing is a crucial link in the entire manufacturing process, especially in high-precision industries such as aerospace, medical equipment and high-end mold manufacturing. The final performance and appearance quality of parts are highly dependent on the quality of the finishing stage.

Different from rough machining, finishing uses a smaller cutting depth (usually between 0.2-1mm) and a lower feed rate (generally 200-800mm/min) to reduce the impact of cutting force on the workpiece and improve surface quality. For example, when machining high-precision molds, I usually use small-diameter tools (such as end mills of 2mm or less) for low-speed finishing to achieve a surface roughness of Ra 0.8μm or even lower. This method can effectively avoid tool marks and improve the finish and fit accuracy of parts.

Characteristics Of CNC Finishing

Compared with rough machining, finishing focuses on detail processing and high-precision machining of parts. Its main features include:

• High Dimensional Accuracy : The dimensional tolerance of fine machining is generally controlled within ±0.01mm or even lower to ensure that the parts meet the assembly requirements. For example, the tolerance of aerospace parts usually needs to be controlled within ±0.005mm to ensure the interchangeability and stability of parts.
• Excellent Surface Quality : The surface roughness after fine machining can usually reach Ra 0.8μm or even Ra 0.2μm to reduce friction and improve the durability of parts. For example, high-end mold processing usually requires a surface finish of Ra 0.2μm or less to ensure mold life and product quality.
• Low Cutting Load : The cutting depth for finishing is usually small (0.1-1mm), which reduces the impact of the tool on the workpiece and prevents deformation or residual stress of the workpiece due to excessive cutting force.
• Use high-precision tools : During finishing, we usually use small-diameter, sharp tools, such as super-hard end mills or PCD (polycrystalline diamond) tools, to improve machining accuracy and reduce tool wear.

Typical Parameters For CNC Finishing

During the finishing process, the processing parameters of different materials are different and need to be optimized according to the specific application. The following are typical finishing parameters for different materials:

Tool Selection For CNC Finishing

Since finishing requires high surface quality, the selection of tools is crucial. The following are common types of finishing tools:

• Superhard End Mill : suitable for aluminum alloy, stainless steel and other materials, the tool has good wear resistance, sharp cutting edge and improves surface quality.
• PCD Tools : Suitable for super-hard materials such as tungsten carbide or ceramic materials, often used in the finishing of aerospace parts.
• Ball End Milling Cutter : suitable for finishing of curved parts, such as smoothing of complex curved surfaces in the mold industry.
• Diamond Tools : used for ultra-precision machining, such as finishing of optical lenses or high-gloss parts, and can achieve mirror effects below Ra 0.2μm.

Surface Treatment Process In Finishing

In some applications, machining alone cannot meet the surface quality requirements of the final product, so we usually combine multiple surface treatment processes to further improve the performance of the parts. For example:

• Polishing : Mechanical polishing or electrolytic polishing is used to make the surface reach a mirror effect. It is often used in medical devices and optical parts.
• Electroplating : A protective layer is applied to the metal surface, such as nickel plating or chromium plating, to improve corrosion resistance and conductivity.
• Anodizing : Commonly used for aluminum alloy parts, oxidation treatment improves wear resistance and corrosion resistance while providing a more aesthetic appearance.
• Sand Blasting : Remove surface burrs by spraying abrasive at high speed to improve the uniformity and wear resistance of the part surface.
• Spraying : Spray coatings such as powder coating or fluorocarbon coating on the surface of parts to improve corrosion resistance and decorative effects.

In a high-precision medical device project I was in charge of , we needed to process a batch of stainless steel surgical instruments. Since surgical instruments require extremely high surface finish and corrosion resistance, we used electrolytic polishing after CNC finishing to reduce the surface roughness from Ra 1.2μm to Ra 0.2μm, and passed the salt spray test to ensure its corrosion resistance. This not only improves product quality, but also extends the service life of the instruments.

Overall, CNC finishing is a critical step to ensure the final quality of parts. Reasonable cutting parameters, tool selection and surface treatment technology can ensure that the product reaches the best state in terms of dimensional accuracy, surface quality and mechanical properties. In high-end manufacturing fields such as aerospace, medical devices, and automotive parts, the optimization of finishing processes can greatly improve product performance and service life. Therefore, finishing is not just a simple processing step, but an important link that determines product quality.

The Core Difference Between CNC Rough Machining And Finishing

CNC machining is divided into rough machining and finishing, and there are significant differences between the two in terms of machining purpose, parameter setting, tool selection, and coolant use. The main task of roughing is to remove material quickly, while finishing focuses on improving dimensional accuracy and surface quality.

Below I will analyze the key differences between the two in detail, and combine practical experience to help you understand how to reasonably select and optimize these two stages in CNC machining :

As can be seen from the table, the focus of rough machining is to remove materials efficiently, while finishing pursues higher dimensional accuracy and surface finish. Therefore, in actual production, we usually use different processing strategies and tools to optimize the processing effects of the two stages.

Key Features Of Roughing

high Material Removal Rate (MRR)
roughing is to remove material as quickly as possible to achieve a near-net shape. Typically, roughing can achieve a material removal rate of 100-500 cm³/min. For example, when machining an aluminum alloy workpiece, I would use a Φ20mm end mill, set the cutting depth to 8mm, and feed at 1500mm/min, which would quickly remove most of the material and significantly reduce the machining time.

Higher Cutting Depth And Feed Rate
In the roughing stage, we usually use a larger cutting depth (5-15mm) and a higher feed rate (500-2000mm/min). This can reduce the number of processing times and improve overall production efficiency. For example, in the roughing of stainless steel parts, I often use a cutting depth of 5mm and a feed rate of 1000mm/min to complete material removal in the shortest time.

Poor Surface Quality
Since the main goal of rough machining is to remove material, surface quality is not a priority. Generally, the surface roughness after rough machining is between Ra 3.2-6.3μm, and subsequent fine machining is required to improve the surface finish. For example, when machining automotive engine parts, the surface after rough machining may have obvious tool marks, so fine machining must be performed to achieve the final quality requirements.

Key Features Of Finishing

High Dimensional Accuracy And Surface Quality
The main purpose of finishing is to improve the dimensional accuracy of parts and obtain a higher surface finish. Usually, the dimensional tolerance of finishing can be controlled within ±0.01mm, or even ±0.005mm. For example, when machining the mold cavity, I use a Φ3mm ball head cutter with a cutting depth of 0.2mm and a feed rate of 300mm/min to make the final surface roughness reach Ra 0.4μm or less, thereby reducing the workload of subsequent polishing.

Lower Cutting Depth And Feed Rate
Finishing uses a smaller cutting depth (0.1-2mm) and a lower feed rate (50-500mm/min) to reduce cutting force and avoid workpiece deformation. For example, when finishing a titanium alloy medical device part, I will use a Φ2mm end mill, set the cutting depth to 0.1mm, and the feed rate to 100mm/min to ensure high precision and high finish of the final product.

Optimize Surface Treatment And Improve Part Performance
Finishing is not just a mechanical cutting process, but also a combination of different surface treatment processes to optimize part performance. For example, when processing high-end aviation parts, we may perform anodizing after finishing to improve the corrosion and wear resistance of the material.

Key Considerations For CNC Roughing

CNC rough machining is the first step in the manufacturing process, and its core goal is to quickly remove materials and improve processing efficiency. However, in actual operation, we need to consider multiple key factors to ensure the stability and cost-effectiveness of processing.

The following are some key factors to focus on during the roughing phase :

Processing Parameters

The core goal of roughing is to increase the material removal rate, so it is crucial to optimize the feed rate, cutting depth and spindle speed. Generally speaking, roughing adopts a high feed and deep cutting strategy to reduce processing time. For example, in aluminum alloy processing, I usually choose the following parameters:

• Feed speed 1500 mm/min
• Cutting depth 6 mm
• Spindle speed 12000 rpm

With such processing parameters, the rough machining of a 300mm × 300mm × 50mm aluminum alloy part can be completed within 10 minutes, which is about 40% higher than the traditional method. In addition, in the rough machining of steel parts, due to the hard material, I will reduce the feed rate to 800-1000 mm/min and increase the cooling amount of the cutting fluid to prevent the tool from wearing too quickly.

Thermal Management And Cooling Fluids

During roughing, a lot of heat is generated during the cutting process due to the large cutting depth and fast feed speed. If the heat is not properly controlled, it may cause workpiece deformation, increased tool wear, and even affect the dimensional accuracy of the part. In order to effectively manage the processing heat, I usually adopt the following strategies:

• The high-pressure cooling system (70 bar) is suitable for rough machining of high-hardness materials (such as stainless steel and titanium alloy), which can effectively remove cutting heat and extend tool life by 30%.
• Choose the right cutting fluid. In aluminum alloy processing, I will use water-based cutting fluid, while in steel processing, oil-based coolant is more effective and can reduce the wear rate of the tool.
• Optimize cutting paths to avoid local overheating. For example, when machining deep cavities, use a layered roughing strategy to remove each layer of material more evenly and prevent excessive heat concentration.

Machine Type And Software

Rough machining requires a highly rigid machine tool, otherwise the tool may be damaged or the workpiece may be deformed due to vibration, affecting the final machining accuracy. In my experience, the following machine tool types are more suitable for rough machining:

• Gantry milling machine, suitable for rough machining of large parts, can reduce vibration and improve cutting stability
• Five-axis machining center can reduce the number of tool changes and improve overall machining efficiency in the rough machining of complex parts

In addition, during CNC programming, I usually use optimized CAM software (such as Mastercam or PowerMILL) to generate reasonable tool paths to avoid tool overload or unnecessary air cutting. For example, in the rough machining of a titanium alloy part, I adjusted the cutting path to reduce the tool load by 15%, extending the tool life and reducing the number of tool changes.

During the rough machining of an aerospace part, I successfully controlled the workpiece temperature below 60°C by using high-pressure coolant, reducing thermal deformation and reducing the dimensional error of the final part by 50%.

Key Considerations For CNC Finishing

The main goal of CNC finishing is to ensure that the final dimensional accuracy, surface quality and mechanical properties of the parts meet the design requirements. Since finishing requires high precision, we must optimize tool selection, machine tool accuracy, surface treatment and other aspects to achieve the best processing effect.

High Precision Size

In finishing, the dimensional accuracy is usually required to be within ±0.01mm, or even stricter. For example, in mold manufacturing, the tolerance of some key components needs to reach ±0.005mm. Therefore, I usually use the following methods to ensure high-precision dimensional control:

• Use high-precision five-axis machining centers, such as Makino, DMG MORI and other brands of high-end machine tools, to provide more stable precision
• Online measurement system, using laser probe or touch probe during processing, real-time detection of part dimensions and automatic adjustment of tool compensation to ensure accuracy remains within the set range
• Low-speed finishing, using low cutting depth (0.1-0.5mm) and low feed rate (50-300 mm/min) to reduce the impact of the tool on the workpiece and improve dimensional stability

For example, when processing aircraft engine turbine blades, I used a five-axis machining center and combined it with online measurement technology, ultimately achieving a dimensional accuracy of ±0.005mm, ensuring that the parts could meet high-precision assembly requirements.

Surface Quality

Finishing is not only for controlling the size, but also for ensuring the surface finish of the parts. In many high-end industries (such as medical, aerospace, optical parts, etc.), the surface roughness requirements are very high, usually need to reach Ra 0.2μm or less. I use the following strategies to optimize the surface quality:

• Using high-precision tools, such as PCD diamond tools or ceramic tools, can reduce cutting marks and improve surface quality.
• Optimize cutting parameters, reduce feed rate to 50-200 mm/min, and reduce each cutting depth to less than 0.1 mm to obtain a smoother surface.
• Subsequent surface treatment, such as mirror polishing, electrolytic polishing, ultrasonic cleaning, etc., further improves the surface quality

For example, in a medical device processing, I used a 0.2mm diameter tool for ultra-precision milling, combined with the electrolytic polishing process, to make the surface roughness of the part reach Ra 0.1μm, meeting medical standards.

Economy And Cost

Finishing usually involves high-end machine tools and high-precision tools, so the processing cost is high. In mass production, I usually use the following methods to reduce costs:

• The tool life monitoring system monitors tool wear in real time to avoid waste caused by premature tool replacement. For example, in the finishing of automotive parts, I extended the service life of a single tool by 20% by optimizing tool life management.
• Optimize the machining path, reduce the tool non-cutting time, and improve the machine tool utilization. For example, when finishing aviation parts, I use a spiral cutting path to reduce the number of tool changes and improve production efficiency.
• Batch production optimization: when processing in batches, arrange the order of tool use reasonably and use fixtures to fix multiple parts at one time to reduce processing time and improve production efficiency.

In a large-scale finishing project, I successfully reduced the unit cost by 15% and improved the overall production efficiency by optimizing the processing path and the use of batch fixtures.

Roughing and finishing play different roles in the CNC manufacturing process. Roughing emphasizes material removal efficiency, while finishing focuses on dimensional accuracy and surface quality. In actual production, we need to reasonably select processing parameters, optimize tool use, control processing heat, and combine appropriate surface treatment methods according to part requirements to ensure that the final product not only meets quality standards but also has good economic benefits. By continuously optimizing processing strategies, we can improve production efficiency and reduce manufacturing costs while ensuring product quality, making CNC processing more efficient and accurate.

FAQs

What Is Roughing In CNC Machining?

Roughing in CNC machining is the initial process of removing excess material quickly to shape the workpiece close to the final form. It typically uses high material removal rates (MRR up to 500 cm³/min), large depth of cut (5-15mm), and high feed rates (1000-3000 mm/min).

What Is The G Code For Roughing?

The G-code for roughing varies depending on the machining strategy. Commonly used codes include G71 (turning roughing cycle), G72 (facing roughing cycle), and G73 (high-speed peck drilling for rough cutting). For milling, G81-G89 cycles may be used depending on the operation.

What Is The Difference Between Roughing And Finishing CNC?

Roughing removes large material volumes at high speeds but results in poor surface finish (Ra 3.2-12.5μm). Finishing uses smaller depth of cut (0.1-2mm) and lower feed rates (50-500 mm/min) to achieve high precision (±0.01mm) and fine surface quality (Ra 0.2-0.8μm).

What Is The Advantage Of Roughing?

Roughing maximizes material removal efficiency, reducing total machining time by up to 40%. It enhances productivity, prolongs tool life by distributing cutting loads, and prepares the workpiece for finishing. In aerospace machining, adaptive roughing can improve efficiency by 30-50%.

How Long Does Rough Carpentry Take?

Rough carpentry timelines vary by project size. A 2,000 sq. ft. residential house typically takes 2-3 weeks, while large commercial buildings may take 2-4 months. Factors include crew size, materials, and complexity. Prefabrication can reduce time by 30% or more.

Conclusion

In CNC machining, roughing and finishing each have different tasks: roughing is responsible for efficient material removal and improving production efficiency, while finishing ensures the dimensional accuracy and surface quality of the final parts. The two complement each other and are indispensable. In my production practice, rationally optimizing the parameters of roughing and finishing can not only improve machining efficiency, but also reduce costs and improve the final quality of parts. I hope this article can help you deeply understand the key differences between roughing and finishing in CNC machining, and find the best process combination in actual production.